Concerning causes and development mechanism of diaper rash, according to “So-Called Diaper Rash” of Kazuya YAMAMOTO described in pages 949 to 956 (1998) of “Clinical of Dermatology” Vol. 30, authored by Kazuya YAMAMOTO, issued by Kinbara Shuppan, (1) ammonia is generated, when urine and stool are mixed, (2) this ammonia sets environment to be alkaline, (3) an enzyme in the stool is strongly activated in an alkaline atmosphere and a weak portion of skin is inflamed by the enzyme and ammonia, and the diaper rash is generated. As a cause for producing the weak portion of the skin, a mechanical stimulus such as touch of a diaper constituting material in contact with the skin, an environment inside the diaper in which the skin is in a puckered state because of high humidity in the diaper, and the like are pointed out.
By capability enhancement with the technical progress of a super absorbent polymer (SAP) against the causes of the above-described diaper rash, for example, discharged urine is quickly absorbed and permeation/diffusion of the urine is minimized. Thereby, it is possible to prevent the urine from being easily mixed with the discharged stool. Moreover, concerning the environment inside the diaper, for example, when an air-permeable sheet is used in the diaper, a countermeasure against a sweaty skin in the diaper is possible, and the skin is effectively prevented from being puckered. With this advancement of the countermeasure against the diaper rash, skin troubles have decreased such as rash generated by use of a so-called disposable diaper.
However, countermeasures have not been sufficient yet for prevention of rash by substantially simultaneously discharged urine and stool, or soft stool. Even when the soft stool is not mixed with the urine, the stool left to stand is a heavy burden on the skin. Since the soft stool hardly passes through a top sheet of the diaper abutting on the skin, a part of moisture shifts to an absorber, but the remaining part remains in the top sheet and sticks to a backside of a wearer. Therefore, even when a trouble is not generated in the skin, a wiping operation of the backside becomes laborious at a time of diaper changing.
To prevent the above-described mixing of the stool and urine or the sticking of the stool to the backside, a diaper which can separate the urine and stool is proposed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 61-41304, Jpn. UM Appln. KOKAI Publication Nos. 6-5614, 6-21623, 6-11723, and Jpn. Pat. Appln. KOKAI Publication No. 10-192339.
In the diaper disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 61-41304, an opening long in a longitudinal direction is disposed in the middle of the top sheet, an elastic member is attached to a peripheral edge of the opening, and arrangements are made such that so-called sturdiness is imparted to the top sheet and the opening is prevented from being closed. Moreover, the diaper disclosed in the Jpn. UM Appln. KOKAI Publication No. 6-5614 includes: a concave portion extending under the opening disposed in a surface sheet; and a valve portion constituted by the surface sheet extended into a middle portion from the periphery of the opening. Arrangements are made such that the stool separated by the opening is prevented from returning. For the diaper disclosed in the Jpn. UM Appln. KOKAI Publication No. 6-21623, two sets of flaps extending in longitudinal and width directions are overlapped with each other, and the opening is formed in the middle of the overlap, so that the area of the opening containing the stool can be set to be large. Furthermore, the diaper disclosed in the Jpn. UM Appln. KOKAI Publication No. 6-11723 includes: a second surface sheet disposed on a first surface sheet; and further a plurality of elastic members for expanding the opening disposed in the middle portion of the second surface sheet in the longitudinal direction in a transverse direction. In the diaper disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 10-192339, a spacer is disposed between the absorber and top sheet, and the opening connected to a space formed by the spacer is formed in the top sheet.
For the diapers disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 61-41304 and Jpn. UM Appln. KOKAI Publication No 6-5614, when actual wearing of the diaper is observed, a crotch region of the diaper is attracted toward the middle by a wearer's legs thigh. It has further been found that the region hangs downwards without closely sticking to the skin. That is, since the crotch region of the top sheet or surface sheet (hereinafter these will be generically referred to as the top sheets) of each of these diapers does not closely stick to a wearer's crotch, the opening disposed in the top sheet does not have any meaning. This causes a disadvantage that the stool spreads over the top sheet. Even if the position of the opening of the top sheet agrees with that of wearer's anus, the top sheet does not closely stick to the wearer's crotch, and the opening is therefore in a closed state. Therefore, it is expected that the stool cannot be guided between the top sheet and a back sheet via the opening.
Moreover, with the diaper disclosed in the Jpn. UM Appln. KOKAI Publication No. 6-21623, when the area of the opening formed in the second surface sheet is set to be large, the position of the opening can substantially securely be aligned with that of the wearer's anus. Conversely, the opening area of the opening is excessively large, the stool is guided between the second surface sheet and first surface sheet via the opening and returns again onto the second surface sheet via the opening, and the wearer's backside may be made dirty in high possibility.
Furthermore, for the diaper disclosed in the Jpn. UM Appln. KOKAI Publication No 6-11723, the opening is expanded only in the width direction, the opening is collapsed by the wearer's crotch, and the sufficient function of the opening cannot basically be fulfilled in the same manner as in the prior art.
In the diaper disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 10-192339, since the space for containing the stool is formed between the absorber and top sheet by the spacer using the elastic material, the spacer is in contact with the wearer's backside via the top sheet. There is a disadvantage that comfort of wear is impaired. Moreover, occupancy of the opening formed in the top sheet is small. Therefore, stool having low fluidity cannot easily pass through the opening of the top sheet quickly, and the wearer's backside may be made dirty.